Objectives: This study was designed to evaluate the psychometric features of the Persian version of the Fatigue Impact Scale [FIS-P] tool when used in Iranian MS patients. Methods: 140 MS patients and the equivalent number of healthy controls completed the following assessments: FIS-P, Fatigue Severity Scale [FSS] , SF-36 questionnaire and the Mini-Mental State Examination [MMSE] .
Results: A significant inverse correlation between FIS and the quality of life [SF-36 assessment tool] , as well as a positive and significant correlation with the FSS were noted. The Intraclass Correlation Coefficient [ICC] values for the inter-rater reliability for the physical, cognitive, and social sections and the whole questionnaire were 0.89, 0.86, 0.95 and 0.98, respectively. The FIS Persian version was shown to possess a high reliability [with a Cronbach’s alpha of 0.953] . Likewise, the ICC values for the testretest reliability were 0.86, 0.87, 0.92 and 0.93 for the physical, cognitive, social subscales and the whole questionnaire, respectively. This suggested a high reliability for the FIS-P.